This invention relates to an overedge sewing machine and more particularly to the guiding of a looper thread to a rotary looper thread take-up in such a sewing machine.
As an example of a conventional-type of looper thread take-up in overedging sewing machines, U.S. Pat. No. 4,492,174 (Kaufmann 1985; titled "Thread Control Mechanism For Sewing Machines") discloses one type of rotary looper thread take-up. Referring to FIG. 3 herein, which is a partial view of the conventional embodiment of FIG. 1 of U.S. Pat. No. 4,492,174, a looper thread T is introduced to a rotary looper thread take-up mechanism 32 from the right side of the drawing of FIG. 3 as shown in the arrow. The thread T is then passed through a looper 24.
Numeral 40 denotes a thread cam and is fixed to a shaft 22. The thread cam 40 is shaped as an eccentric semi-circle as shown in FIG. 4, so that when the shaft 22 rotates clockwise, the looper thread T is drawn from the right side to the rotary take-up mechanism 32.
Referring to FIG. 4, which is a side view drawing viewed from the arrow Y.sub.1 -Y.sub.2 in FIG. 3, and FIG. 5 which is a top view drawing of FIG. 4, the rotary take-up mechanism 32 will now be explained in more detail. Numeral 36 denotes a slot opening provided in a support plate 38. Numerals 42 and 44 denote thread guides having thread eyes provided therein. The thread guides are fixed to the support plate 38 by screws 46. Each thread guide 42, 44 is provided with an oblong hole 48 such that their positions in relation to the support plate 38 may be adjusted. Numeral 50 denotes a stripping finger which is adjustably carried by the plate 38, and is situated between two thread cams 40, such that the thread is moved along the bottom edge of the stripping finger as the thread cams 40 rotate. Accordingly, looper thread feeding is conducted. The rotary looper thread take-up mechanism also works to take-up slack on the looper thread.
However, the aforementioned conventional-types of rotary take-up for the looper thread have the following demerits:
(1) Uneasy guiding of looper thread to the rotary take-up.
Since the rotary thread is eyed through two eyes E.sub.1 E.sub.2, guiding of the looper thread to the rotary take-up is not easy.
(2) Spinning of the looper thread.
When the looper thread becomes broken, the rotating cam 40 picks up the loose thread and winds it up. Often, by the time an operator has noticed the break, a large quantity of thread is wound up, thus requiring a long period of time to remove the wound thread.
According to U.S. Pat. No. 4,492,174, a pneumatic apparatus was provided to direct a stream of air against the rotary take-up, and thus hopefully the loose thread would be prevented from becoming entangled in the rotating shaft. According to another patent, U.S. Pat. No. 4,633,795 (von Hagen 1987; entitled "Looper Thread Control With Anti-Spin Cutting Knives"), when the thread is broken accidentally, a knife, located on at least one side of rotary cam and having a cutting edge disposed generally parallel to the rotational axis, cuts the thread and thus the unnecessary winding up of thread would hopefully be prevented. U.S. Pat. No. 4,325,314 (Niem 1982) discloses an alternative earlier method for breaking an entangled thread.
It is therefore an object of the invention to eliminate the aforementioned and other demerits of conventional rotary looper thread take-ups used for overedging sewing machines.